Mandrel for bending

ABSTRACT

A mandrel for bending of simple construction and sufficient rigidity is obtained. The mandrel comprises a plurality of plugs. Each plug is provided with a spherical outer peripheral surface A fulcrum pin is fitted through the plug. The first and second link members are rotatably attached to the fulcrum pins of the neighboring plugs so as to connect the neighboring plugs. The plug is also provided with a spherical depression which the adjoining plug can enter during the bending. The plugs are connected to the shank via the second link members.

FIELD OF THE INVENTION

[0001] This invention relates to a mandrel for bending which inhibitsformation of irregularities at a bending part of a pipe during thebending process.

BACKGROUND OF THE INVENTION

[0002] Unexamined Japanese Utility Model Publication No. 6-41921 andUnexamined Japanese Patent Publication No. 7-290156 disclose a knownconventional mandrel for bending comprising a plurality of plugs coupledin series onto an end of a shank. As can be seen in FIG. 4, the outerperipheral surface of each plug 50 is formed to be spherical and aconnection shaft 52 is inserted through the center of the plug 50. Theconnection shaft 52 is provided with a spherical part 54 at one end anda spherical depression 56 at the other end.

[0003] The spherical part 54 of the connection shaft 52 is fitted intothe spherical depression 56 of another connection shaft 52, which thusconstitutes an adjustable joint. In this manner, a plurality of plugs 50are connected in series. Moreover, the shank 58 is provided with aspherical depression 60 which is identical to the spherical depression56. The spherical part 54 of the terminal connection shaft 52 is fittedinto the depression 60 so that all the plugs 50 are connected to theshank 58.

[0004] When bending ie performed, the plugs 50 are inserted into a pipe62 to be arranged at the bending part. While the bending is performed,the spherical parts 54 rotate within the spherical depressions 56, 60and the plugs 50 are waggled along the bending direction. As a result,spaces between the respective plugs 50 are narrowed and the outerperipheral surfaces of the plugs 50 are abutted to the inner wall of thepipe 62 in a concentrated manner on the inside of the bend. Thus,formation of irregularities, such as wrinkles, on the inside of the bendis inhibited.

SUMMARY OF THE INVENTION

[0005] However, as shown in FIG. 4, in the case of bending using theconventional mandrel as above, it is necessary to create the sphericalpart 54 at one end and the spherical depression 56 at the other end ofthe connection shaft 52. Such construction is complex and is not easy toproduce. Moreover, the plug 50 has to be fixed to the connection shaft52. There is a problem that sufficient rigidity may not possibly beobtained.

[0006] One object of the present invention is to provide a mandrel forbending having simple construction and sufficient rigidity.

[0007] To attain this and other objects, the present invention providesa mandrel for bending which inhibits formation of irregularities of apipe by arranging plugs at a bending part within the pipe. The mandrelcomprises a plurality of plugs. Each plug is provided with a sphericalouter peripheral surface. A fulcrum pin is fitted through the plug. Alink mechanism is rotatably attached to the fulcrum pins of neighboringplugs for connection therebetween. Each plug is provided with adepression which the adjoining plug can enter during the bendingprocess.

[0008] The mandrel for bending constituted as above is simple inconstruction and can achieve high rigidity.

[0009] The plugs may be connected to a shank via the link mechanism. Thedepressions may be formed to be spherical.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

[0010] The invention will now be described, by way of example, withreference to the accompanying drawings, in which:

[0011]FIG. 1 is a cross-sectional view of a mandrel for bendingaccording to an embodiment of the present invention before bending;

[0012]FIG. 2 is a cross-sectional view taken along the line II-II inFIG. 1;

[0013]FIG. 3 is a cross-sectional view of the mandrel for bendingaccording to the embodiment after bending; and

[0014]FIG. 4 is a cross-sectional view of a conventional mandrel forbending after bending.

DETAILED DESCRIPTION OF THE INVENTION

[0015] As shown in FIG. 1, a pipe 1 is arranged to be brought intocontact with the outer periphery of a bend die 2 which is designed tobend the pipe 1 at a desired angle. Facing to the bend die 2, a clampdie 4 is provided so that the pipe 1 is held between the bend die 2 andthe clamp die 4. While the bending is performed, the bend die 2 rotatesand the clamp die 4 moves around the bend die 2. A pressure die 6 isalso provided in line with the clamp die 4. The pressure die 6 receivesbending reaction force induced while the pipe 1 is being bent.

[0016] A mandrel 10 for bending is inserted into the pipe 1. The mandrel10 is composed of a plurality of plugs 12 and a shank 14. Each plug 12is provided with an outer peripheral surface formed to be spherical. Afulcrum pin 16 is piercingly fitted into the plug 12 through the centerof the spherical outer peripheral surface of the plug 12.

[0017] To the fulcrum pin 16, a link mechanism including a first linkmember 18 and a pair of second link members 20, 22 is rotatablyattached. Both the first and second link members are formed into aplate. In the present embodiment, one end of the first link member 18 isrotatably attached to the fulcrum pin 16 of the plug 12 and the otherend of the first link member 18 is rotatably attached to the fulcrum pin16 of the adjoining plug 12 for connecting the two neighboring plugs 12.

[0018] As can be seen in FIG. 2, one ends of the second link members 20,22 are rotatably attached to the same fulcrum pin 16 to which the otherend of the first link member 18 is attached. The other ends of thesecond link members 20, 22 are rotatably attached to the fulcrum pin 16piercing the adjoining plug 12, to which one end of another first linkmember 18 is rotatably attached. In other words, between the one ends ofthe second link members 20, 22, the other end of the first link member18 is held, and between the other ends of the second link members 20,22, the one end of the another first link member 18 are held, so thatthe two neighboring plugs 12 connected via the first link member 18 arecoupled with another two neighboring plugs 12, connected in the samemanner, via a pair of second link members 20, 22.

[0019] The other end of this another first link member 18 is rotatablyattached to the fulcrum pin 16 of the further adjoining plug 12. Byrepetition of the above, a plurality of plugs 12, that is, four in thepresent embodiment, are connected to each other via the first linkmembers 18 and the second link members 20, 22. Also, a fulcrum pin 24similar to the fulcrum pin 16 is fitted through the shank 14. One endsof the second link members 20, 22 which are connected to the terminalplug 12 at the other ends are rotatably attached to the shank via thefulcrum pin 24.

[0020] Each plug 12 is provided with a spherical depression 26 which theadjoining plug 12 can enter. The spherical depression 26 is formed alittle larger than the spherical outer peripheral surface of the plug12. In the present embodiment, the distance between the fulcrum pins 16of two neighboring plugs 12 is substantially equal to or a little largerthan the radius of the spherical outer peripheral surface of the plug12. Accordingly, the center of the spherical depression 26 and thecenter of the spherical outer peripheral surface of the adjoining plug12 are almost the same. Additionally, the shank 14 is also provided witha spherical outer peripheral surface which is identical to the outerperipheral surface of the plug 12, on the side where there is the plug12.

[0021] The diameter of the outer peripheral surface of the plug 12 is alittle smaller than the internal diameter of the pipe 1 so that the plug12 can be inserted into the pipe 1. The plug 12 is formed by cutting asphere at both ends, leaving a central portion having a thicknesssubstantially equal to the radius of the sphere. A plurality of plugs 12are arranged with a little space therebetween in the thicknessdirection.

[0022] On the side of the plug 12 opposite to the side where there isthe spherical depression 26, a cut-off depression 28 is formed in such amanner that the plug 12, the first link member 18, and the second linkmembers 20, 22 can together rotate on the fulcrum pin 16. In the presentembodiment, the cut-off depression 28 is designed to allow rotation toonly one direction.

[0023] Now, operation of the mandrel 10 for bending of the presentinvention will be explained.

[0024] Firstly, as shown in FIG. 1, a pipe 1 is held between the benddie 2 and the clamp die 4. The pressure die 6 is abutted to the pipe 1.Next, the mandrel 10 for bending comprising a plurality of plugs 12 isinserted into the pipe 1. At the time of the insertion, each plug 12 isdisposed in such a manner that the side with the cut-off depression 28faces to the inside of the bend.

[0025] While the bend die 2 is rotated on its axis, the clamp die 4 isrotated around the bend die 2. As a result, the pipe 1 is wound aroundthe bend die 2, resulting in that the outside of the bend is stretchedand the inside of the bend is compressed at the bending part of the pipe1.

[0026] As shown in FIG. 3, in the mandrel 10 for bending, the plugs 12,the first link members 18, and the second link members 20, 22 togetherrotate on the respective fulcrum pins 16. The spaces between the plugs12 are expanded on the outside of the bend and are narrowed on theinside of the bend. As a result, on the inside of the bend, the outerperipheral surface of the plug 12 moves into the depression 26 of theadjoining plug 12 and the plugs 12 are closely abutted to each other sothat no space is left between the neighboring plugs 12. Accordingly,even if the pipe 1 is compressed on the inside of the bend during thebending, formation of irregularities like formation of wrinkles cannotbe promoted.

[0027] Moreover, the respective plugs 12 are connected via the fulcrumpins 16, the first link members 18, and the second link members 20, 22.Therefore, the construction is simple. Even if large external force isapplied to the respective plugs 12, the plugs 12 are supported by thefulcrum pins 16, the first link members 18, and the second link members20, 22. Accordingly, the rigidity is high enough to be capable ofinhibiting damages.

[0028] The present invention is not limited to the above embodiment, andother modifications and variations are possible within the scope of thepresent invention.

What is claimed is:
 1. A mandrel for bending a pipe, comprising aplurality of plugs, each plug being provided with a spherical outerperipheral surface, a fulcrum pin being fitted through the plug, and alink mechanism being rotatably attached to the fulcrum pins of theneighboring plugs so as to connect the neighboring plugs, wherein eachplug is provided with a depression which the adjoining plug can enterduring the bending process.
 2. The mandrel for bending as set forth inclaim 1, wherein said plugs are connected to a shank via the linkmechanism.
 3. The mandrel for bending as set forth in claim 1, whereinsaid depression is spherical.
 4. The mandrel for bending as set forth inclaim 1, wherein said link mechanism comprises a plate-like first linkmember which connects two neighboring plugs, and a plate-like secondlink member which connects one of said two neighboring plugs withanother plug which adjoins said one of two neighboring plugs.
 5. Themandrel for bending as set forth in claim 4, wherein said second linkmembers are provided in pairs and the first link member is arranged tobe held therebetween.
 6. The mandrel for bending as set forth in claim4, wherein said plug is provided with a rotation restriction mechanismwhich restricts the rotation of the first link member around the fulcrumpin of the plug to regulate a bending direction of the mandrel duringthe bending process.